FOOD PROCESSING & PACKAGING TAKE TIGHT CONTROL IN FOOD TASKS


construction, and partly by using digital signals, in the form of IO-Link, to send data to the control system. In contrast with traditional analogue techniques, the accuracy of signals transmitted via IO-Link are unaffected by electrical noise and have no conversion (A-D) losses, making it possible to achieve exceptional resolution over a very wide measuring range.


Andy Walker, from ifm electronic, explains how new sensing solutions make it easier than ever to keep hygiene and temperature under tight control in the food industry


he top priority of every food manufacturer is product safety. Many factors in the manufacturing process affect safety, but two of the most important are hygiene and temperature. Hygiene of the production plant is an essential requirement, both to ensure product purity and to minimise the risk of cross-contamination when the plant changes over from one product to another. Many modern food manufacturing processes rely on cleaning in place (CIP) to reach the required standards of cleanliness, while keeping the plant downtime needed for cleaning to a minimum.


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CIP, which typically works by introducing cleaning fluids into the plant and then flushing them out again before the plant is returned to service, is an excellent solution, but if it is to work as intended, there are two key requirements. The first is that the concentration of the cleaning solution must be correct, and the second is that all traces of the solution must be flushed from the plant at the end of the cleaning cycle. Failure to satisfy either of these requirements will, at best, lead to product wastage and, at worst, if the problem is not promptly detected, potentially harmful product may reach the market. As might be expected, food


manufacturers put rigorous procedures in place to minimise the risk of these problems


occurring, but a more dependable approach is to directly monitor and measure what’s going on. The most convenient way of doing this is to look at the conductivity of the fluids in the plant. The cleaning fluid, when at the correct concentration, will have a relatively high and known conductivity, whereas the flushing water will have a very low conductivity once all the cleaning fluid residues have been removed. While conductivity sensors are nothing new, what is new is a sensor that can deliver the level of accuracy needed at high conductivity levels to confirm the correct concentration of the cleaning fluid and also at very low conductivity levels to confirm that flushing is complete. The new sensors achieve this partly by advanced design and


As well as helping to guarantee product safety, using a conductivity sensor to monitor CIP can also boost productivity. The reason is simple. With the sensor providing positive confirmation that all cleaning fluid has been flushed from the plant, it is no longer necessary to prolong the flushing process “just to be sure”. This means shorter CIP cycle time, leading to increased plant availability and higher productivity. The sensor will therefore pay for itself very quickly! Let us turn now to temperature, which is one of the most critical aspects of food processing. In techniques like pasteurisation, even marginally incorrect temperatures can lead to serious quality and safety issues. Temperature sensors are commonplace, but here’s a question: if the calibration of a temperature sensor starts to drift, how much product will be compromised before anyone notices? A serious error is likely to be noticed quickly, but even then, there may be considerable product wastage. A more subtle error may persist for some time before detection, which could mean whole batches of product have to be scrapped or even recalled.


The remedy is a new type of temperature sensor that incorporates two sensing elements with opposing (PTC/NTC) characteristics. The sensor constantly compares the measurements from the two sensing elements which, under normal circumstances, match very closely. If a mismatch occurs, indicating calibration drift, this is detected immediately, and the sensor provides a local visual indication as well as sending a warning to the plant control system. These temperature sensors use IO- Link digital communication to ensure that they deliver highly accurate data to the control system. They also feature inherent self-checking capabilities.


The new conductivity and temperature sensors discussed here have been specifically developed for the food industry and therefore comply with all major national and international standards for hygienic applications. Whether used in new plant or as a retrofit upgrade to existing plant, their cost is modest but the benefits they deliver in terms of enhanced product safety and peace of mind, are invaluable.


A new type of temperature sensor from ifm incorporates two sensing elements with opposing (PTC/NTC) characteristics


ifm electronic www.ifm.com/uk


OCTOBER 2021 | PROCESS & CONTROL 31


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